The present invention relates to method and apparatus for deposition of metals, metal alloys and metal-matrix composites upon a substrate. More particularly, the present invention relates to deposition of metals, metal alloys and metal-matrix composites by means of a gas-metal arc deposition process and apparatus.
Aluminum is a widely used structural material which is especially desirable for applications in which high strength to weight ratios are needed. Recent attention has focused on further improving the properties of aluminum alloys by using them as a matrix material in composites. Metal-matrix composites (MMC) have unique mechanical property advantages over pure metals as engineering materials. Materials with high strength and modulus, improved fatigue and wear resistance, and good elevated temperature creep properties can be manufactured, and their properties can be made directional by the appropriate choice of reinforcement shape, volume fraction, and processing. Within the aluminum alloy system, silicon carbide (SiC) is one of the leading reinforcement materials. Aluminum/silicon carbide (Al/SiC) composites are relatively inexpensive and they have high specific strength and specific stiffness that make them candidates for critical aerospace, automotive, and optical applications.
Various techniques are available for coating metals upon a substrate material.
Thermal spraying, also known as flame spraying, involves the heat softening of a heat fusible material such as metal or ceramic, and propelling the softened material in particulate form against a surface which is to be coated. The heated particles strike the surface and bond thereto. A conventional thermal spray gun is used for the purpose of both heating and propelling the particles.
A thermal spray gun normally utilizes a combustion flame, a plasma flame, or an electrical arc to produce the heat for melting of the spray material. It is recognized by those skilled in the art, however, that other heating means may be used as well, such as resistance heaters or induction heaters, and these may be used alone or in combination with other forms of heaters.
The material to be deposited may be fed into the heating zone in the form of powder, or a rod, or wire.
In the wire type of thermal spray gun, the rod or wire of the material to be sprayed is fed into the heating zone formed by a flame or the like, such as a combustion flame, where it is melted or at least heat-softened and atomized, usually by compressed gas. The compressed gas then propels the metal in finely divided form onto the surface to be coated.
In an arc wire spray gun, two wires are melted in an electrical arc which is struck between the wire ends, and the molten metal is atomized by compressed gas, usually air, and sprayed onto a workpiece to be coated. The rod or wire may be conventionally formed as by drawing, or it may be formed by sintering together a powder, or by bonding together the powder by means of an organic binder or other suitable binder which disintegrates in the heat of the heating zone, thereby releasing the powder to be sprayed in finely divided form. In other forms, the wire may have a coating sheath of one component and a core of the others, or it may be made by twisting strands of the components.
Another technique which is suitable for depositing a metal or metal alloy is that of gas-metal arc welding. In gas-metal arc welding, a consumable wire electrode passes through a copper alloy contact tip. Electrical potential applied between the contact tip and the metal to be welded (the base metal) results in a current in the wire which supports an arc between the wire and the base metal. The wire electrode is melted by internal resistive power and heat transferred from the arc. Droplets of molten metal are transferred from the wire to the weld pool of the base metal by a combination of gravitational, Lorentz, surface tension and plasma forces. Heat is transferred to the base metal directly from the arc and also by the molten droplets. Electrode wire, molten droplets, weld pool and solidified weld bead behind the weld pool are protected from oxidation by a shielding gas, such as argon or carbon dioxide. Gas-metal arc welding has been automated by providing means for controlling the rate of filler wire feed and the means for controlling the weld speed (the relative motion between the contact tip and the workpiece). Generally, control of the process has been limited to certain factors which machine builders have been accustomed to, such as the filler wire feed rate, welding speed, current and voltage. These are parameters related to the process.
With this then being the state of the art, it is an object of the present invention to provide a method and apparatus for deposition of metals, metal alloys, and metal-matrix composites upon a substrate.
It is a more particular object to provide a method and apparatus for the deposition of aluminum, aluminum alloys, and aluminum-matrix composites upon a substrate.
These and other objects of the invention, as well as the advantages thereof, will become more clear from the description which follows.